The disclosure relates to a device for limiting a current delivered by a battery strand.
Battery systems are used increasingly as energy stores for both stationary and mobile applications. Examples of the stationary use include wind turbines and emergency power systems, and examples of the mobile use include electric and hybrid vehicles.
Here, battery systems that are based on lithium-ion battery cells are often used. For this purpose a multiplicity of battery cells are generally connected in series to form battery modules. Battery strands are produced by connecting a plurality of battery modules in series. In powerful battery systems, also referred to hereinafter as batteries, a plurality of battery strands are often connected in parallel.
For electrical energy stores with high energy density, battery cells with low internal resistances are especially used, which can deliver relatively high powers with moderate heating. In particular, lithium-ion batteries on account of a very low internal resistance have the property of being able to deliver very high currents compared with previously known batteries. A short-circuit current delivered by a lithium-ion battery thus exceeds those of previously known batteries several times over.
Battery-based energy stores are particularly suitable for networks with high demands on availability, as exist for example in vehicles such as cars or submarines. So as not to impair the availability of these networks in the event of a fault of individual consumers, it is necessary to separate fault sources quickly and reliably from the network in the event of a short circuit. For this purpose, the individual consumers are usually operated via fuses or circuit breakers with electromagnetically actuated overcurrent detection at the network. In order to enable the tripping of these protective elements, the battery system as current source in a network must be able to deliver the necessary short-circuit current. In the case of battery systems with low impedance, the provision of minimal current intensity in order to trip the protective elements is unproblematic. However, the property of such battery systems to deliver extremely high short-circuit currents extremely quickly in the event of a short circuit is critical. A quick, complete separation of the network and battery system is not expedient in this case on account of the loss of the availability of energy. Protection against overload the network can be provided by way of example by an accordingly robust design of the networks with accordingly dimensioned protective elements. Alternatively, arrangements can be used that limit a rise of the current already at the power source, i.e. the battery, in the event of a fault.
A device that is suitable for limiting DC currents in high-energy DC current networks is known from document WO-2010/089338 A2. The short-circuit protection device uses an ohmic resistor to limit the currents. This resistor is connected into the energy path by means of a quick current monitoring and power semiconductors. A current delivered by a battery strands is limited purely digitally by the connection/bridging of the resistor.
A device for controlling a three-phase electric machine, which device has energy stores, connectable in sub-units, in the form of DC voltage sources which can be connected and disconnected and also a downstream inverter, is known from document US 2002/0175644 A1. The connection and disconnection of DC voltage sources is performed by a control unit. A protection device for limiting the current delivered by the energy store in the event of a fault is not described in document US 2002/0175644 A1.
Document WO 2008/055493A1 describes a submarine direct current network with high-energy stores. Here, battery cells and battery modules are connected with as little inductance as possible. A monitoring arrangement for monitoring battery strands is described, which transmits measurement data to a control arrangement and is suitable for deactivating a battery strand.
Semiconductors as protective elements limiting a rise in current are also provided. A control or regulation of a short-circuit current occurring in the event of a fault is not described.
U.S. Pat. No. 6,246,214 B1 describes a protective circuit for the charging of a battery. This protective circuit contains a field effect transistor, which can limit the flow of current when charging or discharging the battery. The circuit additionally contains a discharge regulation system, which is coupled to the field effect transistor and which is able to determine an excessively strong flow of current in the system and to then transmit a signal to the field effect transistor to limit the flow of current. This may be the case in particular when a short circuit is present in the battery. The use of a current converter for this purpose is not described.
U.S. Pat. No. 6,815,930 B2 describes a protective circuit for a battery cell. The protective circuit consists inter alia of a MOSFET transistor, which is connected in series to the battery cell to be protected. When a voltage that is lower than a predefined voltage is measured in the battery cell to be protected, the MOSFET transistor then changes its state and thus limits the flow of current through the battery cell.
Furthermore, document US 2011/0285538 A1 describes an apparatus and a method for determining an abnormality in a compensating circuit for battery cells.
Document US 2002/0079865 A1 describes a protective circuit for a charging unit and a chargeable element, such as a rechargeable lithium-ion battery.